The present invention relates in general to resin injected pultrusion and, more particularly, to an improved resin injection die and methods for performing resin injected pultrusion.
Pultrusion of resin impregnated fibers, such as mineral or glass fibers, is well known. Generally, pultrusion of resin impregnated fibers involves impregnating a multitude of continuous fibers and/or continuous fiber/mat combinations with a suitable resin material and passing the impregnated fibers through a die. Traditionally, the continuous fibers were impregnated by passing the fibers through a bath of liquid resin material, thereby completely wetting or coating the fibers in the resin material. The coated fibers were then consolidated and passed through a pultrusion or cure die where the fibers were formed into a desired shaped and the resin material cured to fix the fibers in place.
However, the resin baths of these prior art processes have several significant drawbacks. Resin baths, as operated in the prior art, resulted in an undue amount of waste of resin material thereby increasing operating expenses. Further, as tanks were employed to hold the resin materials, a large quantity of both time and expense were required to change from one particular resin material to a different type of resin material.
In addition, resin materials, for the most part, comprise blends of organic compounds, a significant portion of which are volatile organic compounds or VOC'S. The emission of VOC's is strictly monitored and limited by various governmental agencies and regulations. Compliance with the regulations can become quite expensive. Resin baths, as employed in the prior art impregnation processes, are open or partially open to the atmosphere and involve the use of large quantities of resin materials. The level of VOC emissions in these prior art processes is much larger than desired.
As a result of the drawbacks to the use of a resin bath to impregnate continuous fibers, resin injection as a means for impregnating continuous fibers in a pultrusion process has been utilized for a number of years. The resin injection process consists of replacing the resin bath and any wet preform stations that may be employed with a machined cavity in a die. As dry fiber is fed through the die and into the cavity, resin is injected such that the fibers are coated with resin material.
U.S. Pat. No. 5,073,413 to Koppernacs et al. discloses a typical prior art resin injection apparatus. Referring to FIG. 3 of the '413 patent, a reinforcement comprising fibers 2 and cloth 6 enter an injection die and are passed into a teardrop-shaped cavity 52 where resin material is injected. The fibers and resin material pass into a tapered portion of the cavity where the combination is rapidly compressed. Unfortunately, some reinforcement packs, especially those having low permeability layers, may not be fully impregnated. This results, it is believed, because the fiber layers are not sufficiently compressed at the point where resin is injected to permit sufficient resin pressure and flow to fully impregnate the fibers. Also, it is believed that the resin pressure along the entire length of the cavity is not sufficiently high to effect complete impregnation of the reinforcement pack. Accordingly, the final pultruded product may have a higher level of voids, i.e., areas in the product in which no resin is present, than desired. Such voids in the final product lead to weak points which result in unsatisfactory performance.
U.S. Pat. No. 3,556,888 to Goldsworthy also discloses a prior art resin injection means. Goldsworthy discloses a composing tube having a tapered entrance through which fibers are passed and resin is injected to impregnate the fibers. Goldsworthy does not disclose a teardrop-shaped cavity in the composing tube as in the '413 patent. Rather, Goldsworthy injects resin into the fibers in the tapered entrance of the composing tube. Furthermore, Goldsworthy separates the composing tube from the curing die. Between the composing tube and curing die, Goldsworthy exposes the impregnated fibers to the atmosphere without being under compression. During this exposure, the fibers may separate such that air is allowed to permeate back into the reinforcement pack creating voids. Thus, Goldsworthy does not reduce the presence of voids.
Accordingly, a need remains for an apparatus for resin impregnated pultrusion wherein tightly compressed bundles of fibers may be completely impregnated and the presence of voids in the final pultruded product reduced.